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Glued laminated timber
Glued laminated timber, also called Glulam, is a type of structural timber product composed of several layers of dimensioned timber glued together. By laminating several smaller pieces of timber, a single large, strong, structural member is manufactured from smaller pieces. These structural members are used as vertical columns or horizontal beams, as well as curved, arched shapes. Connections are usually made with bolts or plain steel dowels and steel plates. Like other engineered wood products, glulam represents an efficient use of available resources. Whilst demand for lumber continues to increase worldwide, the reduction in availability of high-quality, large-diameter logs has combined with environmental concerns and changes in forestry management practices to make larger sections and long lengths of solid timber increasingly less economical and more difficult to procure. Glulam utilises smaller readily available sections that are efficiently end-jointed using bonded finger joints. Glulam is stronger and stiffer than similar-sized members made of solid wood. This is achieved by grading during manufacture, together with the statistical effects of dispersing defects. Glulam also suffers less from movement due to moisture changes in use, because the individual laminations are dried to a close tolerance during manufacture. Glulam is a demonstrably sustainable alternative to concrete and steel. A study by Nabuurs, G.J.; Schelhaas, M.J.; Ouwehand, A.; Pussinen, A.; Brusselen, J. van; Pesonen, E.; Schurck, A.; Jans, M.F.F.W.; Kuiper, L. Future wood supply from European forests; implications for the pulp and paper industry; Alterra-repport CEPI 30 8.doc, Alterra, Wageningen, Netherlands, 2002 was undertaken to quantify the future supply of raw wood from European forests, considering the years 2005 to 2060, with 36 countries included. A forest resource model was tested for two sets of management regimes: “projection of historical management” and “new management trends.” The results indicated that if trends in forest management and supply continue, a theoretical shortfall of 195 million m3 roundwood per annum may occur by 2060 because of demands by the European zone of Russia. However, market adaptations are likely and even taking Russia into account, the total growing stock in European forests will increase from 51 billion m3 in 2005 to 62 billion m3 in 2060. Glulam has much lower embodied energy than reinforced concrete and steel, although of course it does entail more embodied energy than solid timber. However the laminating process allows timber, a generally environmentally benign material, to be used for much longer spans, heavier loads and complex shapes. History One of the earliest still-standing glulam roof structures is generally acknowledged Müller, C. Laminated timber construction, Birkhauser, ISBN 3-7643-6267-7, Basel, 2000 to be the assembly room of King Edward College, a school in Southampton, England, dating from 1870. A church in St Helens, Holy Trinity, Parr Mount, is now thought to have the earliest extant use in the UK (1857). Other examples of 19th-century British glulam have also been identified. The first industrial patented use was in Weimar, Germany. Here in 1872 Otto Hetzer set up a steam sawmill and carpentry business in Kohlstrasse. Beginning in 1892, he took out a series of patents. DRP No. 63018 was for a ventilated timber floor deck that could be tightened laterally after installation, to compensate for shrinkage. Hetzer continued to patent various ingenious systems, but the first of these that could be compared with subsequently standardised horizontal glulam was DRP No. 197773, dated 1906. This entailed vertical columns which transitioned into curved glued laminated eaves zones, and then became sloped rafters, all in a single laminated unit. Each component, bonded under pressure, comprised three or more horizontally arranged laminations. In other words, the glulam portal frame was born. In 1895, Hetzer moved his company to Ettersburger Strasse, still in Weimar. At the height of production, in around 1917, he employed about 300 workers, and Müller includes a fine engraving of the railway sidings and works in 1921 , built using the Hetzer system in 1911.]] In 1909, the Swiss engineering consultants Terner & Chopard purchased permission to use Hetzer's patent, and employed glulam in a number of projects. These included the former Hygiene Institute, Zurich, 1911, now the main building of the university, where the bell-shaped roof dome is still to be seen. The technology arrived in North America in 1934 when Max Hanisch, Sr., who had worked with Hetzer at the turn of the century, formed a firm in Peshtigo, Wisconsin to manufacture structural glued laminated timber. Glulam Bridges As well as being used in buildings, glulam is applied to construct timber bridges. The ability described above to form large cross sections, long lengths and curved shapes makes it advantageous for this purpose. Laminated timber bridges include not only pedestrian footbridges, of which many examples are found, but also road bridges. An example in North America of the latter is at Keystone_Wye, South Dakota, constructed in 1966 - 7. Here two associated glulam arch bridges create a unique interchange having impressive architecture. References See also *Engineered wood *Fiberboard *Hardboard *Masonite *Medium-density fiberboard *Oriented strand board *Particle board *Plywood *Pressed wood *Laminated veneer lumber External links *American Institute of Timber Construction *Glued Laminated Timber Association (UK) *Glulam 'the naturally engineered solution' from BKTS (UK) *Glulam Beam Repair/Reinforcement - An article (Printed in STRUCTURE magazine, Sep. 2006) by Gary W. Gray P.E. and Paul C. Gilham P.E. Category:Composite materials Category:Engineered wood